First Light Survey results confirm excellent performance

The Planck space observatory, ESA’s mission to study the early Universe, has successfully completed its initial test survey of the sky, confirming that both of the scientific instruments and the sophisticated cryogenics, all of which the UK played a key role in building, are working well. Following the successful survey, Planck has now embarked on its 15 month mission to map the structure of the Cosmic Microwave Background radiation (CMB) – the relic radiation from the Big Bang.

A map of the whole sky at optical wavelengths shows a prominent horizontal band which is the light shining from our own Milky Way, seen in profile from our vantage point. The superposed false-colour strip shows the area of the sky mapped by Planck during the First Light Survey. The colour scale indicates the magnitude of the deviations of the temperature of the Cosmic Microwave Background from its average value, as measured by Planck at a frequency close to the peak of the CMB spectrum (red is hotter and blue is colder). The large red strips trace radio emission from the Milky Way, whereas the small bright spots high above the galactic plane correspond to emission from the Cosmic Microwave Background itself. The two squares indicate the location of the detailed images shown in the next figures. Image credit: ESA, LFI and HFI Consortia (Planck); Background image: Axel Mellinger

The ‘first light survey', which started on the 13th August and was a two-week period during which Planck surveyed the sky continuously, produced maps of a strip of the sky, one for each of Planck’s nine frequencies. The plane of our own Milky Way galaxy can be seen running across the middle of the image, and is visible in the Planck data as the bright red regions. Away from the plane, the tiny fluctuations in the CMB can shine through, and these are the main target of the Planck mission.

The properties of the tiny fluctuations in the CMB provide information about the earliest moments of the Universe's existence and how it evolved to become the Universe we see today. Planck is looking with finer resolution and greater sensitivity than previous satellites, and will allow the details of the Universe's age and composition to be calculated more precisely than ever before.

A zoom on a 10°x10° region of the First Light Survey where the Milky Way is not the predominant signal shows clearly the features which are of most interest to Planck, i.e. the Cosmic Microwave Background. In the left and right panels are observations by LFI at 70 GHz and one detector of HFI at 100 GHz respectively. At each of these frequencies the dominant emission is the CMB, and both maps indeed show very similar features. The small visible differences are expected, due to the still imperfect calibration at this early stage of processing, and to remaining low-level galactic emission. The fact that two completely independent detectors based on different technologies are so quickly able to yield maps of such remarkable similarity is a powerful confirmation of Planck’s ability to detect and map the very faint CMB structures arising in the early Universe.Image credit: ESA, LFI and HFI Consortia (Planck)

By observing at all 9 frequencies, Planck can separate the CMB from the light emitted by the Galaxy at the same frequencies. As a result, Planck will make unprecedented observations of our own Galaxy, detecting and characterising both gas and dust. Having maps at all nine frequencies allows the individual sources of microwave light to be distinguished better than ever before.

The above mosaic of maps zooms in on a small part of the First Light Survey, in which our own Milky Way shines very brightly. The nine panels show a 20°x20° map of the emission imaged by Planck in each of the nine frequencies that it is sensitive to: 30 GHz (top left) to 857 GHz (bottom right). Each strip is slightly offset from the others due to the arrangement of the detectors in the focal plane. At low frequencies electrons in the Milky Way emit radio waves as they interact with gas and the magnetic field; at high frequencies it is dust that radiates heat. At each frequency a different mix of radiation processes contributes to the structure visible in the images; the combination of frequencies provides a rich source of information on the physics of our Milky Way – much of it never available until now. Image credit: ESA, LFI and HFI Consortia (Planck)

Professor George Efstathiou of the University of Cambridge and UK Principal Investigator for Planck said, `We are thrilled that Planck is working so well. Scientists in the UK were involved in building the two focal plane instruments on Planck and also critical parts of the sophisticated cooling system. We have now begun scientific analysis of the beautiful data from Planck and are looking forward to finding out new information on the beginnings of space and time as we know it.'

Professor Richard Davis of Manchester University and principal investigator of the UK's contribution to Planck's LFI instrument said, “In the 16 years since Planck’s development started, this is the most exciting time. The wonderful thing is that Planck from its vantage point one million miles from Earth is now producing images of the creation of the Universe, the so-called Big Bang, with a clarity never seen by mankind.”

Professor Peter Ade of Cardiff University and the UK HFI Instrument Scientist said: “This short set of data has already shown more detail in two weeks than we got from 5-years of WMAP data – Planck is set to make fantastic discoveries.”

The Planck satellite was launched along with the Herschel satellite on 14th May 2009 from Kourou, French Guiana, on an Ariane 5 rocket. During its 6 week journey to its observation point around L2, 1.5 million km (1 million miles) from Earth, the scientific instruments were cooled to extremely low temperatures, making Planck the coldest object in space at just 0.1° above absolute zero (-273.15°C). It took around 6 weeks for Planck to cool down to these low temperatures, after which a further 6 weeks were spent calibrating the instruments.

Routine operations started as soon as the First Light Survey was completed, and surveying will now continue for at least 15 months without a break. In approximately 6 months time, the first all-sky map will be assembled. [Update: this image is now available here.]

Within its allotted operational life of 15 months, Planck will be able to gather data for two full independent all-sky maps. To fully exploit the high sensitivity of Planck, the data will require a great deal of delicate adjustments and careful analysis. It promises to contain a treasure trove of data that will keep both cosmologists and astrophysicists busy for decades to come.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council, which provides the UK funding for Planck, said, "It’s great news that Planck is operating so effectively. UK researchers have invested a great deal of time and skill in this mission and we are all eager to find out what secrets Planck will reveal."